[IDK_Melaphystos]

Ok, assume you have two components that, when mixed, create and endothermic reaction (like Ammonium Nitrate and Water). Now answer these questions:

(1) After the mixture has absorbed all the heat, what exactly remains? Something like Nitrous Oxide or whatnot (for this example)?

(2) What would one have to do to get the fundamental products back; or rather, what would one have to do to make the substance absorb more heat (recycle the reaction)?

These questions aren't just limited to Ammonium Nitrate and Water, but all endothermic counterparts.

Thanks in advance

[Yggdrasil]

The chemical reaction that is going on is:

NH₄NO_{3 (s)} --> NH₄⁺_(aq) + NO₃^-_(aq)

In this case, the energy needed to break the ionic bonds in the ammonium nitrate lattice is more than the energy gained from the solvation of the ammonium and nitrate ions.  However, the reaction goes forward nonetheless because it is driven by the increase in entropy gained by disolving the highly ordered crystal lattice of the salt. 

Until the solution becomes saturated with the salt, the process is irreversible.  Counterintuitively, you could recover some of the disolved salt by cooling the solution, since this will decrease the solubility of the salt in water and may cause some of the salt to precipitate out of solution.  The easiest way to recover the salt, though is to boil off the water.

[edit: thanks for noticing the mistake xiankai]

[xiankai]

In this case, the energy needed to break the ionic bonds in the ammonium nitrate lattice is less than the energy gained from the solvation of the ammonium and nitrate ions.

err, mistake?

[Yggdrasil]

Yes, it was a mistake.  Its now corrected.  Thanks xiankai.